The present invention relates to a consumable electrode type pulsed arc welder using a shielding gas of CO.sub.2 gas as its main composition, and a controlling method for the same.
Recently, a consumable electrode type pulsed arc welder using a shielding gas mainly comprising CO.sub.2 gas which is less expensive than a prior inert gas (e.g., argon gas) has been used widely. This consumable electrode type pulsed arc welder using CO.sub.2 gas has advantages of low running cost and forming a superior welded joint. In this kind of consumable electrode type pulsed arc welder, it is required to suppress spatter generation as a technological problem to be solved. It is known that the spatter generation can be decreased by dividing a single pulse into a plurality of different pulses.
A conventional consumable electrode type pulsed arc welder disclosed in unexamined and published Japanese patent application TOKKAI (Hei) No. 1-254385 for example will be explained with reference to FIGS. 8A and 8B concretely.
FIG. 8A is a schematic view showing the relation between a pulse waveform and the conditions of a droplet and an arc at a tip of a wire in the conventional consumable electrode type pulsed arc welder. FIG. 8B is a schematic view showing the relation between another pulse waveform and the conditions of the droplet and the arc at the tip of the wire in the conventional consumable electrode type pulsed arc welder. In FIGS. 8A and 8B, (a) to (h) are drawings illustrating the conditions of a droplet 54 and an arc 57 at a tip of a wire 53 at the respective times a to h on each time-base axis of pulse waveforms.
In the conventional consumable electrode type pulsed arc welder, as shown in FIG. 8A, a first pulse current 51 and a second pulse current 52 larger than the first pulse current 51 are output alternately at predetermined intervals to the wire 53 as a consumable electrode. The second pulse current 52 melts the tip of the wire 53, so as to form the droplet 54 at the tip. In addition, the second pulse current 52 drops the droplet 54 in an arc-area generating the arc 57, so that the droplet 54 is transferred into a weld pool 56 on a base metal 55.
The first pulse current 51 controls the behavior of the weld pool 56 by using its arc force in order to prevent the droplet 54 formed and grown by the second pulse current 52 from shorting against the weld pool 56 during the period from the time b to the time h in FIG. 8A. That is, in the conventional consumable electrode type pulsed arc welder, the arc force generated by the first pulse current 51 prevents the weld pool 56 from approaching the droplet 54 formed at the tip of the wire 53, thereby preventing a short circuiting between the droplet 54 and the weld pool 56. This is evident from the fact that when the first pulse current 51 is not output, the droplet 54 formed by the second pulse current 52 is grown further by the next second pulse current 52, resulting in contacting and short-circuiting to the weld pool 56 as shown in FIG. 8B.
In the conventional consumable electrode type pulsed arc welder, as has been explained in the above, the arc force generated by the first pulse current 51 is used to control the behavior of the weld pool 56. Therefore, the output of the first pulse current 51 is required to satisfy the following conditions (I) and (II).
(I) The arc force can control the behavior of the weld pool 56 approaching the tip of the wire 53. PA1 (II) The droplet 54 is not transferred from the tip of the wire 53 to the base metal 55.
In other words, in the conventional consumable electrode type pulsed arc welder, the first pulse current 51 is required to be adjusted to have a value enough to control the behavior of the weld pool 56 but smaller than that of the second pulse current 52.
However, in the conventional consumable electrode type pulsed arc welder, two pulse currents having different values are required to be output as described above. Thereby, the arc-area is in an unstable state wherein the droplet 54 is dropped and transferred from the tip of the wire 53 to the base metal 54. As a result, in the conventional consumable electrode type pulsed arc welder, the droplet 54 is not dropped and transferred stably but resulting in the spatter generation.